Comparison of one year of XCH4 and XCO measurements using a EM27/SUN low resolution FTIR spectrometer to S5P/TROPOMI methane and carbon monoxide columns at Thessaloniki, Greece

The column-averaged dry air mole fractions of carbon dioxide (XCO2), methane (XCH4) and carbon monoxide (XCO) have been measured for the first time for a whole year in Thessaloniki, Greece, using the portable Bruker EM27/SUN ground-based low-resolution Fourier Transform spectrometer, provided by the Karlsruhe Institute of Technology. The EM27/SUN is a reliable, easy-to-deploy, mobile, low-cost supplement to the Bruker IFS 125HR, a high-resolution spectrometer used in the Total Carbon Column Observing Network (TCCON). Approximately 30 of the EM27/SUN instruments constitute the Collaborative Carbon Column Observing Network (COCCON), with stations around the globe for the quantification of local sinks and sources, working as an important supplement of TCCON to increase the global density of column-averaged greenhouse gas observationsOne year of measurements of XCH4 and XCO are presented for Thessaloniki, Greece. The station is located in the center of the city. The data are compared to collocated measurements from S5P/TROPOMI using 50km and ±30 min as criteria. For the XCH4 comparisons, the ground based XCH4 is constantly found to be lower than the satellite product. However, for ground based retrievals of XCH4 using the TROPOMI algorithm and IR band, the comparison with the satellite data shows a percentage difference lower than ±2%, well within product requirements. Satellite XCO is also compared to ground observations to examine if EM27/SUN concentrations are reproduced by S5P/TROPOMI and whether the temporal variations are captured AknowledgmentsThis work was co-funded by ESA within the Contract No. 4000117151/16/l-LG “Preparation and Operations of the Mission Performance Centre (MPC) for the Copernicus Sentinel-5 Precursor Satellite”. The satellite data were obtained through Sentinel-5P Expert Users Data Hub (https://s5pexp.copernicus.eu/). This research was co-funded by the project "PANhellenic infrastructure for Atmospheric Composition and climatE change" (MIS 5021516) which is implemented under the Action "Reinforcement of the Research and Innovation Infrastructure", funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund).